| Protein lysine acetylation has emerged as a key posttranslational modification in cellular regulation, in particular through the modification of histones and nuclear transcription regulators.In the first part, we use tandem liquid chromatography-tandem mass spectrometry (LC/LC-MS/MS) to analyse the affinity-purified acetylated peptides from cytoplasmic fraction of human liver tissues and found that lysine acetylation is a prevalent modification in enzymes that catalyze intermediate metabolism. Virtually every enzyme in glycolysis, gluconeogenesis, the tricarboxylic acid (TCA) cycle, the urea cycle, fatty acid metabolism, and glycogen metabolism was found to be acetylated in human liver tissue. Our study reveals that acetylation plays a major role in metabolic regulation.In the next three parts, we reported PEPCK1 which is a gluconeogenesis enzyme to elucidate the effect of acetylation on metabolic pathways. Whereas most glycolytic steps are reversible, the reaction catalyzed by pyruvate kinase is irreversible and the reserve reaction requires phosphoenolpyruvate carboxykinase (PEPCK1) to commit for gluconeogenesis. Here we show that acetylation regulates the stability of the gluconeogenic rate limiting enzyme PEPCK1, thereby modulating cellular response to glucose. High glucose destabilizes PEPCK1 by stimulating its acetylation. PEPCK1 is acetylated by the P300 acetyltransferase and this acetylation stimulates the interaction between PEPCK1 and UBR5, a HECT domain containing E3 ubiquitin ligase, therefore promoting PEPCK1 ubiquitinylation and degradation. Conversely, SIRT2 deacetylates and stabilizes PEPCK1. These observations represent the first example that acetylation targets a metabolic enzyme to a specific E3 ligase in response to metabolic condition changes. Given that increased levels of PEPCK is linked with type II diabetes (T2D), this study also identifies potential new therapeutic targets for diabetes. |
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